Skip to content


ai  101  pytorch  classification  nvidia  cuda  install  tensorrt  yolo  ardupilot  None  ros2  dds  micro ros  xrce  sitl  plugin  SITL  debug  rangefinder  pymavlink  mavros  gazebo  distance sensor  system_time  timesync  cmake  gtest  ctest  cpp  c++  format  fmt  multithreading  spdlog  camera  coordinate system  orb  matching  opencv  build  transformation  computer vision  homography  optical flow  of  trackers  cv  cyclonedds  eprosima  fastdds  simulation  config  ignition  bridge  sdf  tips  ign-transport  sensors  lidar  aptly  apt  encryption  pgp  docker  git  bundle  github  hooks  pre-commit  lxd  container  lxc  x11  profile  vscode  marpit  presentation  marp  markdown  mermaid  video  ffmpeg  gstreamer  cheat-sheet  sdp  v4l2loopback  gi  snippets  cheat Sheet  python  asyncio  future  click  cli  numpy  project  template  black  isort  docs  project document  docstrings  flake8  linter  git-hook  mypy  unittest  pytest  pylint  mock  iterator  generator  logging  tuple  namedtuple  typing  annotation  pyzmq  zmq  msgpack  action  namespace  remap  control2  ros2_control  gdb  qos  tag  plugins  msg  node  zero-copy  shm  tutorial  algorithm  calibration  diff  pid  dev  colcon  colcon_cd  rpi  arm  qemu  settings  behavior  plot  visualization  debugging  diagnostic  diagnostics  tutorials  gst  math  apm  rat_runtime_monitor  web  rosbridge  vue  binding  discovery  gazebo-classic  launch  spawn  cook  gps  imu  ray  gazebo_ros_ray_sensor  ultrsonic  range  ultrasonic  gazebo classic  wrench  effort  odom  ign  gz  xacro  ros_ign  diff_drive  odometry  joint_state  argument  OpaqueFunction  DeclareLaunchArgument  LaunchConfiguration  tmux  nav  slam  test  rclpy  executor  MultiThreadedExecutor  SingleThreadedExecutor  param  dynamic-reconfigure  service  client  setup.py  package.xml  parameter  parameters  custom  msgs  executers  pub  sub  rqt  rviz  rviz2  pose  marker  tf2  deb  package  setup  local_setup  rosdep  package manager  project settings  vcstool  cross-compiler  nano  texture  tmuxp  rootfs  embedded  zah  linux  rm  ubuntu  ip  ss  network  netstat  snap  deploy  ssh  systemd  mkdocs  extensions  socat  networking  serial  udp  tc  mtu  select  px4  robotics  kalman_filter  kalman  filter  control  todo  vscode-ext  json  yaml  schema  yocto  poky  world  gazebo_ros2_control  position_controller  effort_controller  velocity_controller  urdf  gazebo_ros_force  gazebo_ros_joint_state_publisher  robot_state_publisher  joint_state_publisher  projects  vrx  buoyancy 

Minimal Pub/Sub with namespace and remapping topics


LAB#

  • Create minimal Pub/Sub with different topic
  • remapping topic from command line
  • remapping from launch
  • add namespace
  • change node name

Minimal nodes#

minimal_pub.py
import rclpy
from rclpy.node import Node
from std_msgs.msg import String

TOPIC = "simple"
PERIOD = 1

class MyNode(Node):
    def __init__(self):
        node_name="minimal_pub"
        super().__init__(node_name)
        self.__pub = self.create_publisher(String, TOPIC, 10)
        self.__timer = self.create_timer(PERIOD, self.__timer_handler)
        self.__timer
        self.__counter = 0
        self.get_logger().info("run simple pub")

    def __timer_handler(self):
        self.__counter += 1
        msg = String(data="pub counter: {}".format(self.__counter))
        self.__pub.publish(msg)

def main(args=None):
    rclpy.init(args=args)
    node = MyNode()
    rclpy.spin(node)
    node.destroy_node()
    rclpy.shutdown()

if __name__ == '__main__':
    main()
minimal_sub.py
import rclpy
from rclpy.node import Node
from std_msgs.msg import String

TOPIC = "simple1"

class MyNode(Node):
    def __init__(self):
        node_name="minimal_sub"
        super().__init__(node_name)
        self.__sub = self.create_subscription(String, TOPIC, self.__sub_handler, 10)
        self.__sub
        self.get_logger().info("start minimal sub")

    def __sub_handler(self, msg: String):
        self.get_logger().info(msg.data)

def main(args=None):
    rclpy.init(args=args)
    node = MyNode()
    rclpy.spin(node)
    node.destroy_node()
    rclpy.shutdown()

if __name__ == '__main__':
    main()
setup.py
# Add entry points
entry_points={
        'console_scripts': [
            "minimal_pub=py_tutorial_pkg.minimal_pub:main",
            "minimal_sub=py_tutorial_pkg.minimal_sub:main"
        ],
    }

first run#

terminal1
ros2 run py_tutorial_pkg minimal_pub
terminal2
ros2 run py_tutorial_pkg minimal_sub
terminal3
# nodes
ros2 node list
/minimal_pub
/minimal_sub

# topics
ros2 topic list
/parameter_events
/rosout
/simple
/simple1

# info topic /simple
ros2 topic info /simple
Type: std_msgs/msg/String
Publisher count: 1
Subscription count: 0

# info topic /simple1
ros2 topic info /simple1
Type: std_msgs/msg/String
Publisher count: 0
Subscription count: 1

usage remapping sub topic#

terminal2
ros2 run py_tutorial_pkg minimal_sub --ros-args -r simple1:=simple
terminal3
ros2 topic list
/parameter_events
/rosout
/simple

launch with remapping#

run_minimal_1.launch.py
from launch import LaunchDescription
from launch_ros.actions import Node

def generate_launch_description():
    ld = LaunchDescription()

    pub_node =  Node(
            package='py_tutorial_pkg',
            executable='minimal_pub'
        )

    sub_node =  Node(
            package='py_tutorial_pkg',
            executable='minimal_sub',
            remappings=[
                ('/simple1', '/simple'),
            ]
        )

    ld.add_action(pub_node)
    ld.add_action(sub_node)
    return ld
terminal1
ros2 launch py_tutorial_pkg run_minimal1.launch.py
terminal2
# nodes
ros2 node list
/minimal_pub
/minimal_sub

# topics
ros2 topic list
/parameter_events
/rosout
/simple

Add namespace#

terminal1
ros2 run py_tutorial_pkg minimal_pub --ros-args -r __ns:=/demo
terminal2
ros2 run py_tutorial_pkg minimal_sub --ros-args -r __ns:=/other_demo
terminal3
# nodes
ros2 node list
/demo/minimal_pub
/other_demo/minimal_sub

# topics
ros2 topic list
/demo/simple
/other_demo/simple1

remap pub this time#

terminal1
ros2 run py_tutorial_pkg minimal_pub --ros-args -r __ns:=/demo -r /demo/simple:=/other_demo/simple1
terminal3
# nodes
ros2 topic list
/demo/other_demo/simple1
/other_demo/simple1

# topics
ros2 topic list
/other_demo/simple1

with launch file#

  • Add namespace
  • Remap topic with full namespace
run_minimal_2.launch.py
from launch import LaunchDescription
from launch_ros.actions import Node

def generate_launch_description():
    ld = LaunchDescription()

    pub_node =  Node(
            package='py_tutorial_pkg',
            executable='minimal_pub',
            namespace="/demo",
            remappings=[
                ('/demo/simple', '/other_demo/simple1'),
            ]
        )

    sub_node =  Node(
            package='py_tutorial_pkg',
            executable='minimal_sub',
            namespace="/other_demo"

        )

    ld.add_action(pub_node)
    ld.add_action(sub_node)
    return ld